After 10 years of mysterious white oak deaths, experts still looking for answers

AMANA — Despite deploying thousands of tests and running samples, researchers still haven’t determined why so many white oak trees across Iowa have died.

Tivon Feeley, forest health program leader with the Iowa Department of Natural Resources, said although Iowa researchers have been “casting a broad net” of tests to help determine what is causing the decline, he said it will likely be another two years before researchers can come to a conclusion.

“We’re running endless tests,” Feeley said, adding that he and his team at the DNR have conducted tests on close to 6,000 samples of Iowa oak trees looking for oak wilt — a fatal disease caused by a fungus that blocks the tree's water-conducting system. He said about 174 of those tests were deployed this year.

The increased tree testing comes as white oak trees have been continuing to decline across the state, a persistent trend that researchers, foresters and woodland owners have been seeing for more than a decade.

Tim Krauss has witnessed the decline firsthand.

Krauss is one of the two foresters with Amana Forestry, in Amana, the largest privately-owned timber land in the state, spanning 7,000 acres.

Krauss said he has seen an increase in the number of seemingly healthy white oak trees that are dying off, especially since the August 2020 derecho. Krauss said he and Amana Forestry’s other forester, Sabrina Keiper, have recorded about 500 white oak tree deaths per year. He said the number of tree deaths has increased 10 to 15 percent each year.

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“Some trees, as you would watch them over the years, they would start to look bad. The next year they’d look a little worse, and third year they’d be dead,” he said. “You'd see that a lot, but then you'd also see trees where, you looked at that same tree last year and it was perfect, and this year it was totally dead.”

Most of the time, he said there wouldn’t be a direct cause for the healthy trees to die off in the span of one year.

Stress on trees

Mark Vitosh is a district forester with the Iowa DNR, overseeing Linn, Benton, Iowa, Jasper, Johnson, Muscatine and Poweshiek counties.

He said the trees that have been lost to the mystery illness were healthy. They weren’t “suppressed” by other larger trees.

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“These are trees that are of mature age, 120 plus (years old) and they’re quality,” he said. “They're trees that you would expect to be healthy and dominant, so some pretty large trees that we're losing.”

Vitosh said there are several environmental factors that could cause a tree to die off or not be able to regenerate.

He pointed to droughts Iowa has seen over the past several years, including one that stretched from July 2020 until the summer of 2024. The four-year dry spell was the longest drought in Iowa since the 1950s.

This summer, though, the state has received more precipitation than normal. July and August, specifically, were exceptionally wet.

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“Even though we've had good moisture, when we have these stressful events, trees don't recover just from one episode of good moisture,” Vitosh said. “Even though we're having good moisture this year, they could still be having challenges out there, because they're stressed to a certain degree, and that just because we're having good moisture doesn't mean they're going to totally recover.”

Vitosh said just because Eastern Iowa has had “decent moisture this year,” doesn’t mean it’s “out of the woods.”

Joe Herring, a DNR district forester who’s based in Iowa Falls, said “erratic swings” between dry conditions and wet years also can stress trees, especially more mature ones.

He said these swings “mess up the internal carbon balance of the tree,” which refers to the way that a tree exchanges carbon dioxide with the atmosphere.

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Herring said another stressor for white oak trees can be insects that find their way into the tree’s bark and roots.

He said researchers have been finding high populations of a native insect called the two-lined chestnut borer. The insect is typically found at the root crown or the base of the tree.

It’s “highly unusual and just a sign of the really high levels of stress going on,” Herring said.

A possible economic hit

With the loss of so many oak trees due to drought, insects or other problems, Krauss said he believes there will be a “major impact” economically for the state.

“I’d say we’ve lost 50 percent of our high-end, highly valuable trees,” Krauss said. “In another 20, 30 years, I would say we will probably (lose) more like 75, 80 percent, so it’ll be a huge economic impact, not just for us, but for anybody selling white oak in Iowa.”

Currently, Krauss said that white oak is one of — if not the — “hottest” woods in Iowa. He said that walnut is another popular wood, but the wood from walnut trees won’t sustain the timber industry in Iowa.

Generally, Krauss said white oaks sell for $200 to $800 per tree. He added that the average price per board foot at Amana Forestry tends to be higher because foresters do the harvesting.

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Recruiting help

As experts continue the work to pin down a cause of white oak deaths, Iowa researchers, foresters and woodland owners are turning to a forestry coalition that focuses on sustaining white oak trees across the United States.

Researchers, foresters and representatives from the White Oak Initiative met in Amana in August to discuss what could be behind the decline, ways to better manage Iowa forests, and what the environmental landscape of white oaks across the country looks like.

Jason Meyer, executive director of the White Oak Initiative, went out with Iowa foresters on Aug. 27. He said the event in Amana wasn’t supposed to solve the decline, but to learn more about the issues they see within Iowa and how they compare to other states seeing white oak deaths.

Meyer said the Initiative exists because data has shown that while there still are many mature white oak trees thriving, many seedlings are not regenerating, creating a twofold issue as healthy trees also are dying off.

He said there are reasons why white oaks aren’t regenerating.

Between tree changes that affect how much sunlight the white oaks receive, and the lack of traditional prescribed burns, Meyer said the white oaks will continue to decline rapidly over the next several decades.

“It's just been very, very difficult to try and figure this thing out,” Krauss said.

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues. She is also a contributing writer for the Ag and Water Desk, an independent journalism collaborative focusing on the Mississippi River Basin.

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Comments: olivia.cohen@thegazette.com